Protective relays are commonly used in electric utility applications to detect various possible problems in the electrical power output and thus protect expensive equipment such as motors and generators. Protective relays continuously monitor power systems to assure maximum continuity of electrical service with minimum damage to life and property.
Some of today's protection applications are, without limitation: motor, generator, transformer, station-bus, line and circuit, system ground, network systems, pilot wire, pilot channel, transmission line, pilot relying, backup, reclosing, synchronizing, load-shedding, frequency and many more. Typically, protective relays, meters and instruments receive their input signals from sensors (commonly current transformers and potential transformers) which step down the high current and voltages and provide a proportional output signal.
The relay terminals are connected to the transformers/sensors through a test switch terminal or “poles”. Each test switch can be associated with one or more relays. Test switches provide the necessary short circuiting of line and load terminals when the relay is removed from its case or the adjacent test switch is opened. In this manner, the test switch disconnects the protective relay from the sensors for the purposes of calibration and/or replacement. Thus, test switches are the means by which protective relays are disabled. Additionally, test switches provide an access point for maintenance personnel to directly measure current/potential values using meters, for example, test plugs.
An exemplary prior art test switch assembly is shown in FIG. 1 and generally indicated by the numeral 10. The wide variety of test switches available allows for many types of applications. As is well known to those of ordinary skill in the art, these applications may include test switches with all potential switches, all current switches or some combination thereof.
Test switch assembly 10 includes on its front face 10 switches 12a to 12j arranged in five (5) sets. In the embodiment shown in FIG. 1 for prior art test switch 10 there are two switches, namely switch 12a and 12b, which are associated with a respective current transformer (not shown). Test switch 10 also includes eight (8) potential switches, namely switches 12c and 12d, 12e and 12f, 12g and 12h, 12i and 12j. 
One example of a pair of switches associated with a current transformer is shown in FIGS. 2a and 2b. The paired switches include a switch, such as switch 12a which has a shorting blade 14 having a handle 26 (switch 12a, when unpaired, may be a potential switch) and a switch 12b which does not have a shorting blade and instead includes a test jack 16. The input from the current transformer is connected to the bottom connector 17 of switch 12a. The electrical current travels through shorting blade 14 and out the top connector 18 of switch 12a, which is in turn electrically connected to a relay. The electrical current travels back from the relay, to top electrical connector 19, through test jack 16 and back to the current transformer through the bottom electrical connector 20 of switch 12b. A shorting tab 22 extends from the bottom of switch 12b to a location beneath switch 12a. Shorting tab 22 is electrically connected to bottom connector 20 of switch 12b. 
During normal operation, with the shorting blade 14 closed, electrical current flows from the current transformer to, bottom connector 17, through the shorting blade 14, to the top connector 18 and from there to the relay. The electrical current returns from the relay through to connector 19, through the test jack 16, to the bottom connector 20, and from there, to the transformer. If, however, an operator wishes to remove the current signal from the relay, the shorting blade 14 is opened. As the blade 14 is rotated, and before it is electrically disconnected from top connector 18, a bottom edge 24 of shorting blade 14 engages the shorting tab 22, thereby electrically connecting bottom connector 17 with bottom connector 20. Thereafter, the blade 14 disconnects from top connector 18 and the current signal to the relay is stopped. By shorting out the circuit first, the current always has a path to travel, thereby preventing dangerous voltage buildup in the transformer.
On the rear face of test switch assembly 10, twenty terminals are provided for connection to the relays and sensors/transformers. When test switch 10 is mounted in a switchboard panel (not shown) the switches 12a to 12j are accessible from the front of the panel and the terminals on the rear face are only accessible from the rear of the panel.
Though prior art test switches have proved remarkably dependable, drawbacks persist. For example, in some instances a maintenance person could disable a relay (via the test switch), for troubleshooting or maintenance purposes. The power system may be restored and the test switch unintentionally left in a configuration that disables the device. Such conditions could cause the protection and control equipment to fail.
Other potential issues exist that may affect relay performance, such as blown fuses, changed wires, or changes to the topology of the protection and control scheme (either intentional or unintentional). Any of these conditions may lead to incorrect operations or failures of the relay. It is therefore desirable to verify all the correct signal inputs to the test switch prior to restoration of the power system.